Albin gropes



A. GRUPER.

MICROPHONE.

Patented Jan. 23, 1894.

UNITED STATES PATENT OFFICE.

ALBIN GRPER, OF DUSSELDORF, GERMANY.

MICROPHONE.

SPECIFICATION forming part of Letters Patent No. 513,181, dated January23, 1894.

Application filed January 14, 1893- Serial No. 458,398- (No model.)

a To all whom it may concern.-

Be it known that I, ALBIN GR6PER, of Dusseldorf, in the Kingdom ofPrussia and German Empire, have invented a new and useful Microphone, ofwhich the following is a specification, reference being had therein tothe accompanying drawings.

This invention relate to improvements in microphonic telephonetransmitters, or those in which variation of the resistance of theelectric circuit in which they are placed is caused bysubjecting bodiesof carbon through which such circuit passes to various pressures; andhas for its object the construction of a transmitter which shall becapable of accurately transmitting the sound of words spoken into it toa great distance and at the sametime be free from external or secondarysounds or noises.

, In the drawings hereunto annexed Figure '1 illustrates in verticalsection one form of telephone transmitter according to my invention,Fig. 2 being a cross section through same, taken on the line A, B,Fig. 1. Fig. 3 illustrates a modified form of the instrument shown atFig. 1, and Fig. 4 is a cross section of same, taken on the line C, D,Fig. 3.

With reference to the drawings, 6 and d are metallic plates carryingbetween them the ebonite ring 9 to which they are screwed. A recess isformed in the ring g for the reception of an india rubber washer b,andmica diaphragm a. The diaphragm d is the first to receive the soundwaves entering the transmitter, and measures about 0.04 millimeters inthickness and is therefore influenced by the slightest sound wave. Thecarbon diaphragm b is separated from abyan air space 0, and thus thevibrations of a. aretransmitted to b and .the carbon balls a aresubjected to greater or less pressure alternately. The current passes byway of the diaphragm 1), balls 0, case h, and plate (1.

A case it is attached to the rear plate d for the reception of thecarbon balls 0. The case h may be formed in various shapes. For instanceit may be rectangular and provided with inclined shelves 8 as shown inFigs. 1 and 2, or be of solid form and circular in shape, as shown inFigs. 3 and 4, and provided with holes or cavities for the reception ofthe carbon balls. In the form of case shown at Figs. 1 and 2, theinclined surface of the shelves 8 is utilized for keeping the balls 0 inloose contact with the diaphragm I), while in the form of case shown inFigs. 3 and 4 this is effected by means of a carbon plate a and springm, the force exerted by the spring being regulated by the nut and bolt1".

Having now particularly described and ascertained the nature of my saidinvention and in what manner the same is to be performed, I declare thatwhat I claim is- In a telephone transmitter of the type described, thecombination of a mica diaphragm and a carbon diaphragm arranged with airspace between them, the mica diaphragm being adapted to receive soundwaves and to transmit them to such carbon diaphragm, and a number ofcarbon balls normally in contact with such carbon diaphragm, wherebysuch carbon balls are subjected to varying pressures and the electriccurrent passing through them to a varying resistance; subs'tantially asand for the purposes herein set forth.

In witness whereof Ihave hereunto set my hand in presence of twowitnesses.

ALBIN GROPER. Witnesses:

D. J. PARTELLO, GUYER LOHR.

